Merge pull request #28193 from ProvableHQ/fix/empty-struct

[Fix] Informative error on empty struct.

compiler/passes/src/type_checking/check_program.rs

@@ -153,6 +153,10 @@ impl<'a, N: Network> ProgramVisitor<'a> for TypeChecker<'a, N> {
                 };
             check_has_field(sym::owner, Type::Address);
         }
+        // For structs, check that there is at least one member.
+        else if input.members.is_empty() {
+            self.emit_err(TypeCheckerError::empty_struct(input.span()));
+        }
 
         if !(input.is_record && self.scope_state.is_stub) {
             for Member { mode, identifier, type_, span, .. } in input.members.iter() {

errors/src/errors/type_checker/type_checker_error.rs

@@ -879,4 +879,11 @@ create_messages!(
         msg: format!("The async function `{name}` does not exist."),
         help: Some(format!("Ensure that `{name}` is defined as an async function in the current program.")),
     }
+
+    @formatted
+    empty_struct {
+        args: (),
+        msg: "A struct must have at least one member.".to_string(),
+        help: None,
+    }
 );

tests/expectations/compiler/structs/empty_struct_fail.out

@@ -0,0 +1,5 @@
+---
+namespace: Compile
+expectation: Fail
+outputs:
+  - "Error [ETYC0372112]: A struct must have at least one member.\n    --> compiler-test:4:5\n     |\n   4 |     struct Bar {}\n     |     ^^^^^^^^^^^^^\nError [ETYC0372083]: A program must have at least one transition function.\n    --> compiler-test:1:1\n     |\n   1 | \n   2 | \n   3 | program test.aleo {\n     | ^^^^^^^^^^^^\n"

tests/tests/compiler/structs/empty_struct_fail.leo

@@ -0,0 +1,12 @@
+/*
+namespace: Compile
+expectation: Fail
+*/
+
+program test.aleo {
+    struct Bar {}
+
+    function main() -> bool {
+        return true;
+    }
+}